1. Field of the Invention
The present invention relates to electrophotographic photosensitive members and more particularly to those having photosensitive layers containing disazo pigments.
2. Description of the Prior Art
As photoconductive materials for use in electrophotographic photosensitive members, there have been known inorganic substances such as selenium, cadmium sulfide, and zinc oxide. These photoconductive substances have many advantages, for example, chargeability to a suitable potential in a dark place and dischargeability also in a dark place, on the other hand, these have also the following disadavantages. For example, in selenium type photosensitive members, the crystallization of photoconductive substance is readily promoted by heat, moisture, dust, pressure, or other factors, remarkably in particular, when the atmosphere surrounding photosensitive member exceeds a temperature of about 40.degree. C., crystallization is more pronounced, whereby there may be caused such disadvantages as lowering in charge bearing properties or formation of white spots on images. In the cases of selenium type and cadmium sulfide type of photosensitive members, stable durability cannot be secured when being allowed to stand under high humidity conditions. Zinc oxide type of photosensitive members requires the sensitization with sensitizing dyestuff typified by Rose Bengal, which causes the charge deterioration caused by corona charging and colour fading caused by light exposure. Therefore, this type of photosensitive members cannot provide stable images throughout a long period of operation.
On the other hand, various kinds of organic photoconductive polymers including poly (vinylcarbazole) in the first place and low-molecular organic photoconductive substances such as 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole have been proposed. It is difficult to use actually these materials, in spite of their superiority in lightness to the above-said inorganic photoconductive materials. The reason for the unsuccessfulness is that these organic photoconductive substances are inferior to inorganic ones in sensitivity, durability, and stability to the change of surrounding conditions.